Undesired evaporative emission detection routines may be intermittently performed on a vehicle fuel system and emissions control system to confirm that the systems are not degraded. Undesired evaporative emissions detection routines may be performed while the engine is running using engine intake manifold vacuum. However, for hybrid-electric vehicles, engine run time may be limited. As such, undesired evaporative emissions detection routines may be performed when the vehicle is off using engine-off natural vacuum (EONV) generated due to a change in temperature and pressure within the fuel tank following engine shutdown and/or with vacuum supplemented from a vacuum pump. If the systems are sealed from atmosphere, a pressure or vacuum will develop there within responsive to changes in ambient temperature if the systems are intact.
Such routines rely on a functional fuel tank pressure transducer (FTPT) to measure the pressure or vacuum within the fuel system. As such, the rationality of the FTPT must be periodically tested and confirmed. The FTPT may be tested for offset, to determine if a baseline output of the FTPT is accurate. One example approach for an FTPT offset test is shown by Jentz et al. in U.S. Patent Application 2015/0075251. Therein, the fuel tank is vented to atmosphere for a lengthy vehicle-off soak. If the FTPT is functional, a value within a threshold of atmospheric pressure should be output following the vehicle-off soak. A deviation from atmospheric pressure may result in a diagnostic trouble code (DTC) being set at the controller, and/or may result in the FTPT output being adjusted to compensate for any offset.
However, the inventors herein have recognized potential issues with such systems. As one example, venting the fuel tank to atmosphere may result in fuel vapor trafficking to a fuel vapor canister. For vehicles with limited engine run-time, opportunities for purging the fuel vapor canister to engine intake may be limited. This could increase evaporative emissions if a saturated fuel vapor canister is exposed to multiple diurnal cycles. If the engine must be forced on to purge the canister, the fuel efficiency of the vehicle may be reduced.
In one example, the issues described above may be addressed by a method for a hybrid-electric vehicle, wherein a fuel tank is sealed closed during a first condition that includes an inductive charging event, and wherein degradation of a fuel tank pressure transducer is indicated responsive to a fuel tank pressure transducer output failing to increase above a threshold following an active testing duration. The outer walls of the fuel tank may include ferrous components which are energized by a magnetic field generated during the inductive charging event, thus heating the fuel tank and the fuel stored within. In this way, the pressure within the sealed fuel tank increases during the inductive charging event, and a determination may be made as to whether the output of the fuel tank pressure transducer is rational.
As one example, such an active fuel tank pressure transducer rationality tests may be indicated following one or more indeterminate passive fuel tank pressure transducer rationality tests. Passive fuel tank pressure transducer rationality tests typically compare fuel tank pressure transducer output with ambient temperature over a vehicle-off soak. However, if the vehicle is operated in a location with a modest diurnal cycle, the ambient temperature may stay relatively constant during a vehicle-off soak. By indicating an active test during an inductive charging event, the fuel tank pressure can be controllably adjusted without requiring additional hardware, and without increasing undesired evaporative emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.